Very often I hear from people who want to visit a spa while in Paris. Here are a few to choose from:

“Comfort Zone”
This spa in the Marais offers four types of massages: “the oriental”, “the Arab”, “the Indian” and “the Mediterranean”. Sauna and hammam are also available.
49 rue Quincampoix
Paris 75004
011 33 1 44 78 64 64

L’Appartement 217
Yes, this spa is in a Parisian apartment. Here you can get a Japanese bath to detoxify the body, a shiatsu massage and even facials. Tres chic.
217 rue Saint-Honoré
Paris 75001
011 33 1 42 96 00 96

Spa Anne Fontaine
This place screams fashion and style. Even the treatments scream style: “Dream of Silk” and “Softness of Cotton”. Enjoy exotic fruits after your treatment!
370 rue Saint-Honoré
Paris 75001
011 33 1 42 61 03 70

Four Seasons Spa
In a word, luxury. If you have the cash, spend it here!
31, ave. George V
75008 Paris
011 33 1 49 52 70 00

Spa Guerlain
This is an institute as well as a spa, so you get good care and great treatments.
68 Ave. des Champs-Elysées
Paris 75008
011 33 1 45 62 11 21